1. Technical Field
The present invention relates to a clamping apparatus of the type that moves a clamp rod linearly to a clamping position after having rotated it from a retreated position to an unclamping position, and more particularly to a technique making it possible for a clamping spring to perform a strong clamping.
2. Explanation of Earlier Technology
Generally, a rotary clamping apparatus of this type is adapted to drive a clamp rod to a clamping position by pressurized oil supplied to an actuation chamber for clamping (for example, see Japanese Patent Publication No. 49-41550).
Although the foregoing prior art is excellent in that it can effect a strong clamping by the pressure of a fluid such as pressurized oil, it has a problem that when the fluid pressure within the actuation chamber for clamping disappears due to fluid leakage or the like, clamping force also disappears.